https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31485
--- Comment #25 from Joel Yliluoma <bisqwit at iki dot fi> --- (In reply to Jakub Jelinek from comment #24) > on x86 read e.g. about MXCSR register and in the description of each > instruction on which Exceptions it can raise. So the quick answer to #15 is that addps instruction may raise exceptions. Ok, thanks for clearing that up. My bad. So it seems that LLVM relies on the assumption that the upper portions of the register are zeroed, and this is what you said in the first place.